It’s important to go back and review your old work. Just a little time away from it and you can look at it with fresh eyes. Enough time away from it and you can look at it with someone else’s eyes.
Getting to the point where you can evaluate a piece of work without any emotional attachment whatsoever, even if it’s only for a brief moment, is incredibly valuable. Not only can you more easily and objectively spot flaws, you can decide what shouldn’t even have your name on it. When you’ve just suffered to produce something, when you’ve poured hours and hours and hours into it, it’s very difficult to say, “Nope, this sucks. Trash it.” But, sometimes it does suck. And that’s OK, most of your work is going to suck. But, it’s important to recognize it when it sucks. You don’t want to be constantly publishing work that sucks.
So reviewing your old work, culling the stuff that obviously sucks, will not only improve the quality of the work you have floating around out there, but it will also improve your skill. Any time spent critiquing work, identifying why it works, why it doesn’t, how it could be improved, etc., is going to sharpen your skills, whether the work you’re critiquing is your own or somebody else’s. The added benefit of critiquing your own work is the possibly of remembering the thought process behind the choices you made, or the obstacles that prevented you from doing something else. This in turn creates a more immediate lesson that you can draw from (e.g. next time you’re painting, you’ll know not to do X, since the last time you did X, the result sucked. This makes the lesson much more tangible than reading about the way Picasso did it.)